Low Power High Gain Radio Frequency Amplifier For Sensor Apparatus

ABSTRACT

A wireless communication device is presented for use with a sensor. The wireless communication device includes: an antenna, a driver circuit and a bias circuit. The driver circuit is electrically coupled to the antenna and includes at least one pair of cross-coupled transistors. The bias circuit is electrically coupled to the driver circuit. In a transmit mode, the bias circuit biases the driver circuit with a first bias current. In response to the first bias current, the driver circuit oscillates the antenna. In a receive mode, the bias circuit biases the driver circuit with a second bias current, such that the first bias current differs from the second bias current. In response to the second bias current, the bias circuit amplifies a signal received by the antenna.

GOVERNMENT CLAUSE

This invention was made with government support under grant numberCNS1111541 awarded by the U.S. National Science Foundation. Thegovernment has certain rights in the invention.

This application claims the benefit of U.S. Provisional Application No.62/454,118, filed on Feb. 3, 2017. The entire disclosure of the aboveapplication is incorporated herein by reference.

FIELD

The present disclosure relates to transceivers for millimeter-scalesensor devices.

BACKGROUND

A wireless sensor network is an example of network in which one or moresensor devices communicate with each other and/or a gateway. As anexample, a micro- or millimeter-scale sensor device may be arranged indifferent locations in a room to detect an environmental condition, suchas temperature, light. The sensor devices may transmit a data signalindicative of the condition to a gateway (e.g., a computer) by way of awireless communication interface disposed within the sensor device.

With technological advancements, the size of the sensor device, whichcan include a battery, has reduced in recent years. As a result,technical challenges posed by mm-scale devices can include conservationof power while enabling long range non-line of sight wirelesscommunication. To increase the communication range of the sensor device,the communication device can utilize power amplifiers and/or low noiseamplifiers, for transmitting or receiving signals. However, suchelectronic components can consume a significant amount of power, andtherefore, require a larger battery.

This section provides background information related to the presentdisclosure which is not necessarily prior art.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

A wireless communication device is presented for use with a sensor. Thewireless communication device includes: an antenna, a driver circuit anda bias circuit. The driver circuit is electrically coupled to theantenna and includes at least one pair of cross-coupled transistors. Thebias circuit is electrically coupled to the driver circuit. In atransmit mode, the bias circuit biases the driver circuit with a firstbias current. In response to the first bias current, the driver circuitoscillates the antenna. In a receive mode, the bias circuit biases thedriver circuit with a second bias current, such that the first biascurrent differs from the second bias current. In response to the secondbias current, the bias circuit amplifies a signal received by theantenna. More specifically, the second bias current has a magnitude setto substantially cancel resistive loss of the antenna and the first biascurrent has a magnitude larger than the second bias current.

In one embodiment, the driver circuit may be further defined as a pairof NMOS field effect transistors cross-coupled to each other and coupledin parallel with the antenna. Alternatively, the driver circuit isdefined as a first pair of NMOS field effect transistors cross-coupledto each other and coupled in parallel with the antenna, and a secondpair of PMOS field effect transistors cross-coupled to each other andcoupled in parallel with the antenna, wherein the bias circuit biasesthe first pair of NMOS field effect transistors. The driver circuit mayalso be defined as a Colpitts oscillator.

The wireless communication device may further include a frequency tuningcircuit electrically coupled in parallel with the antenna, such that thetuning circuit includes at least one capacitor electrically coupled inparallel with the antenna.

In some embodiments, the wireless communication device is integratedinto a sensor device, where the sensor device includes the antennasandwiched between two circuit boards, the driver circuit is mounted toone of the two circuit boards and the bias circuit is mounted to one ofthe two circuit boards.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only, and are not intended tolimit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1 is a diagrammatic view illustrating a wireless sensor networkhaving multiple sensor devices in communication with a gateway;

FIG. 2 illustrates a block diagram of a sensor device;

FIG. 3 illustrates an example structural architecture of the sensordevice;

FIG. 4 is a block diagram of a communication device of the sensordevice;

FIG. 5 is an example of a rectifier for the communication device of FIG.4;

FIG. 6 is an example of a demodulator for the communication device ofFIG. 4;

FIG. 7 is an example of a driver circuit and a bias circuit for thecommunication device of FIG. 4;

FIG. 8 is a graph that illustrates a performance characteristic of anantenna with respect to a bias current;

FIG. 9 is a diagrammatic view illustrating an example sensor initiationprotocol;

FIGS. 10A and 10B are graphs depicting the tuning range and effectiveradiated power, respectively, for the transmitter;

FIG. 11 is a graph depicting sensitivity as a function of bias current;

FIG. 12 is a graph depicting blocker tolerance at different offsets;

FIG. 13 is a generic implementation for the driver-bias circuit; and

FIGS. 14A and 14B are schematics for alternative embodiments of drivercircuits suitable for use in the communication device.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION

Millimeter-scale sensor devices include a wireless communication devicefor exchanging data with other devices, such as other sensor devicesand/or gateway devices. Conventionally, such sensor devices can belimited in non-line of sight long range wireless communication due to,for example, antenna efficiency and/or power limitation of the batteriesprovided in the device.

FIG. 1 illustrates an example wireless network 100 in which mm-scalesensor devices or sensor apparatuses 102 communicate with a gateway 104.The wireless network 100 may be, for example, an internet-of-thingswireless network, an autonomous vehicular network, and/or other suitablenetworks in which small-scale drivers (i.e., nodes) exchange data withanother device and/or a central system (e.g., a gateway).

The sensor devices 102 may also be referred to as sensor nodes and maydetect dynamic properties of the environment in which the sensor deviceis positioned. With reference to FIG. 2, a given sensor device 102 mayinclude a communication device 202, a sensor controller 204, a sensor206, and a power source 208. The communication device 202 of the presentdisclosure increases the long distance communication range of the sensordevice 102, as described in detail below.

In an example embodiment, the sensor controller 204, in conjunction withthe sensor 206, may output data regarding a dynamic property detected bythe sensor 206. For example, the sensor 206 may include photovoltaic(PV) cells for detecting light and may output a voltage indicative ofthe amount of light detected. The sensor controller 204, in return,transforms the voltage into a data signal to be transmitted to thegateway 104 by way of the communication device 202. Alternatively, thesensor 206 may be configured to detect other dynamic properties, such aspressure, temperature, etc. The sensor controller 204 may also receiveinformation from the gateway 104, such as a communication request, byway of the communication device 202. The sensor controller may include,for example, a processor and a computer-readable medium that storesinstructions executed by the processor.

The power source 208 supplies electric power to the components of thesensor device 102. In an example embodiment, the power source 208 mayinclude a battery 210 and a power management unit (PMU) 212. The battery210 may be a thin film battery of, for example, four volts. The PMU 212may distribute power to other components in the sensor device 102.

The communication device 202 establishes wireless communication, such asRF communication, with external devices within a communication range ofthe sensor device. In the example embodiment, the communication device202 includes an antenna 214, a transceiver 216, and a communicationcontroller 218.

In an example embodiment, the antenna 214 is a magnetic dipole antennathat may be coupled to a resonant circuit to improve the efficiency ofthe antenna 214. Alternatively, the antenna can be an electric dipoleantenna, but such an antenna may require a larger resonator circuit toaddress the high impedance of the antenna, thereby increasing the sizeof the communication device 202 and, as a result, the sensor device 102.

The antenna 214 is operable as a receive (i.e., a receive mode) and atransmitter (i.e., a transmit mode) by way of the communicationcontroller 218. The communication controller 218 is communicably coupledto the sensor controller 204 and controls the various electricalcomponents of the communication device 202 to transmit and receive data.For example, when the sensor controller 204 outputs a data signal, thecommunication controller 218 may operate the antenna 214 in the transmitmode by way of the transceiver 216 and, when a data signal is not beingtransmitted, the communication controller 218 may operate the antenna214 in the receive mode to receive signals from other devices.

In an example embodiment, the transceiver 216 includes a bias circuit220 and a driver circuit 222. The bias circuit 220 is electricallycoupled to the driver circuit 222 and is operable by the communicationcontroller 218 to output a bias current to the driver circuit 222. Moreparticularly, the bias circuit operates, in a transmit mode, to bias thedriver circuit with a first bias current, and operates, in a receivemode, to bias the driver circuit with a second bias current, such thatthe first bias current differs from the second bias current. In responseto the first bias current, the driver circuit oscillates the antenna. Inresponse to the second bias current, the driver circuit amplifies asignal received by the antenna as further described below.

FIG. 3 illustrates an example of a sensor device 300 that is, forexample, 3×3×3 mm³. The sensor device 300 is an example of the sensordevice 102. In an example embodiment, the sensor device 300 includes athree-dimensional magnetic antenna 302 disposed between a first circuitboard 304 and a second circuit board 306. An electronic chip stack 308and various electronic components (e.g., capacitors C1, C3, and C4 inFIG. 4) are disposed on a surface of the second circuit board 306 thatis opposite to the antenna 302. The electronic chip stack 308 isconfigured to include the communication device and the sensorcontroller, described herein. The antenna 302 is electrically coupled tothe chip stack 308 by way of terminals 310. The sensor and the batteryof the power source (not shown) are disposed on a surface of the firstcircuit board 304 opposite the antenna 302. Multiple through-connections312 (i.e., vias) are provided to electrically couple the electroniccomponents on the second circuit board, such as the chip stack 308, withthe electronic components on the first circuit board, such as the sensorand battery.

By utilizing the magnetic dipole antenna 302, the electronics of thesensor device 300 may be stacked on top and/or bottom of the antenna302, thus enabling compact integration of the components. Conversely, anelectric dipole antenna typically requires physical separation from theelectronic components, and may therefore increase the size of the sensordevice 300. While a specific structural architecture of the sensordevice is described and illustrated, it should be appreciated that thecomponents of the sensor device may be arranged in various suitableways, and should not be limited to the arrangement illustrated in thefigures.

FIG. 4 illustrates an example embodiment of the communication device202. In the example embodiment, the antenna 402 is a 3D magnetic dipoleantenna having a 4-loop configuration constructed from two copperlayers. The antenna 402 is connected to a transceiver 404 by way of acapacitor C1, which is a surface-mount device and may have a capacitanceof, for example, 0.5 pF. Other types of inductive antennas are alsocontemplated by this disclosure.

The transceiver 404 is an example of the transceiver 216 and, in theexample embodiment, the transceiver 404 includes a variable capacitorC2, a driver-bias circuit 406, a current limiter 408, an amplifier 410,a rectifier 412, a demodulator (DM) 414, and a baseband controller 416.The amplifier 410, the rectifier 412, and the demodulator 414 may bepart of a receiver circuit for processing an incoming signal received bythe antenna 402 in the receive mode. For the purpose of brevity,specific electronic components that are part of a transmitter circuitfor processing a signal to be transmitted by the antenna 402 are notillustrated. Thus, while specific electronic components are illustrated,it should be appreciated that the transceiver 404 may include otherelectronic components.

The variable capacitor C2 may be an integrated digitally-switchedcapacitor array (e.g., a metal-insulator-metal (MIM) capacitor array)and forms a resonant tank with the antenna and capacitor C1. In anexample embodiment, the resonant tank has a quality-factor (Q) of 110 at915 MHz. A resonant frequency of the antenna 402 is tuned using thevariable capacitor C₂ within, for example, a range of 891.4-932 MHz.

The driver-bias circuit 406 is electrically coupled to the currentlimiter 408 and includes the driver circuit and the bias circuit, asdescribed below. Based on a control signal from the baseband controller416, the driver-bias circuit 406 operates the antenna in the receivemode to receive a signal or in the transmit mode to transmit a signal.

With reference to FIG. 13, the driver-bias circuit 406 may be viewedgenerically as a negative resistance circuit 13. One example embodimentof a negative resistance circuit is a pair of cross-coupled transistors.The pair of cross-coupled transistors may be configured to oscillate theantenna or amplify the signal received by the antenna as describedbelow. In another example embodiment, the negative resistance circuitcan be implemented by a single-ended Colpitts oscillator as shown inFIG. 14A or can be implemented by a differential Colpitts oscillator asshown in FIG. 14B. Other implementations for driver-bias circuit 406 arealso contemplated by this disclosure.

In an example embodiment, the amplifier 410 may be a two-stage amplifierthat amplifies the RF signal received by the antenna 402. For example,the amplifier 410 may amplify the signal by 17dB. The rectifier 412 maybe a 32-stage passive rectifier that converts the incoming AC signal toDC signal. FIG. 5 illustrates an example implementation for therectifier 412. The demodulator 414 demodulates the DC signal from therectifier 412 and may include 4 sample-hold (S/H) capacitors and 2clocked comparators. An example implementation of the demodulator 414 isillustrated in FIG. 6. In operation, the output from the rectifier 412is sequentially sampled by S/H capacitors. Once two capacitors (e.g.,C_(s1) & C_(s2) or C_(s3) & C_(s4)) store the voltage for the 1^(st)-and 2^(nd)-half periods of an incoming binary PPM symbol, an associatedcomparator (Comp₁ or Comp₂) generates a demodulated bit. Accordingly, anaccurate reference voltage for the comparator may not be needed.

The baseband controller 416 is an example of the communicationcontroller 218 and may include a processor that executes pre-storedfirmware. The baseband controller 416 controls operation of electroniccomponents of the transceiver 404, such as the driver-bias circuit 406,to transmit a signal via, for example, ON-OFF keying or receiving asignal.

FIG. 7 illustrates an example of the driver-bias circuit 406. Thedriver-bias circuit 406 includes a bias circuit 700 and a driver circuit702. The bias circuit 700 is an example of the bias circuit 220, and thedriver circuit 702 is an example of the driver circuit 222. In addition,in FIG. 5, the antenna 402 is represented by inductor L, capacitorC_(ANT), and resistor R. The resistor R represents a loss of the antenna402. The inductor L and the capacitors Cl and C2 form an LC resonanttank. In the receive mode, the resonant tank may increase thequality-factor (Q) of the antenna 402 and, therefore, further amplifythe signal received by the antenna 402.

In the example embodiment, the driver circuit 702 include two pair ofcross-coupled transistors. That is, the driver circuit 702 includes afirst pair of cross-coupled transistors 704 and a second pair ofcross-coupled transistors 706. The first pair of cross-coupledtransistors 704 is comprised of p-channel transistors P1 and P2;whereas, the second pair of cross-coupled transistors 706 is comprisedof n-channel transistors N1 and N2. The transistors P1, P2, N1, and N2may be field effect transistors, such as MOSFETs. While the exampleembodiment is shown with two pair of cross-coupled transistors, it isreadily understood that the circuit may be implemented with only onepair of cross-coupled transistors arranged either on the high side orlow side of the antenna.

Transistors P1, P2, N1, and N2 are connected to form two invertingamplifiers around the antenna 402. For example, the gate terminals oftransistors P1 and N1 (i.e., control terminals) are electrically coupledto each other to form the input terminal of a first inverting amplifier,and the drain terminals of the transistors P1 and N1 are electricallycoupled to each other to form the output terminal of the first invertingamplifier. The input terminal of the first inverting terminal is coupledto a first terminal 710 of the antenna 402 and the output terminal ofthe first inverting terminal is coupled to a second terminal 712 of theantenna 402. Transistors P2 and N2 are connected in a similar manner toform a second inverting amplifier, where the input terminal of thesecond inverting amplifier (i.e., gate terminals of transistors P2 andN2) is connected to the second terminal 712 of the antenna 402 and theoutput terminal of the second inverting amplifier (i.e., drain terminalsof transistor P2 and N2) is connected to the first terminal 710 of theantenna 402.

The communication controller 218 (e.g., baseband controller 416)operates the antenna 402 in the receive mode or in the transmit mode bycontrolling the bias circuit 700 and, more particularly, the biascurrent applied to the driver circuit 702. In an example embodiment, thebias circuit 700 includes a first current source 718 to generate thefirst bias current and a second current source 716 to generate thesecond bias current less than the first bias current. For example, thesecond current source 716 may output a bias current that is less than orequal to 20 μA and the first current source 718 may output a biascurrent that is greater than or equal to 100 μA.

The specific current value and/or range for values of the first biascurrent and the second bias current may be determined based on theperformance characteristics of the antenna 402. More particularly, thefirst bias current is selected so that the antenna oscillates when thedriver circuit 702 receives the first bias current. On the other hand,the second bias current is selected so that the antenna is dampened toreduce noise when the driver circuit 702 receives the bias current. Inparticular, second bias current has a magnitude set to substantiallycancel resistive loss of the antenna and thereby increase quality factorduring the receive mode. In one example, the second bias current is setproportional to square root of the resistive loss. Accordingly, theperformance characteristic of the antenna 402 may be used to select theappropriate bias current for the transmit mode and the receive mode.

By way of example, FIG. 8 is a graph depicting the voltage gain andantenna power vs. bias current. To operate the antenna in the receivemode, the bias current should be within the Q-enhanced region, and tooperate the antenna in the transmit mode, the bias current should bewithin the oscillation region. In selecting the optimal bias current forthe receive mode, the bias current should be high enough to achieveoptimal voltage gain in order to substantially counter the resistiveloss of the antenna but low enough to prevent oscillation of theantenna.

One method for selecting the bias current may include tuning the antennato the meta-stable region by gradually increasing the bias current untilthe antenna begins to oscillate, and then reducing the bias current by apredetermined amount until the antenna is no longer oscillating. Forexample, the bias current can be gradually increased, and when thedemodulator outputs all ‘1’, it is determined that the antenna isoscillating and the bias current can be reduced by, for example, 10 μA.Basically, once the antenna begins to oscillate (e.g., the meta-stableor oscillation region), the bias current may be reduced in predeterminedincrements (e.g., 5 μA, 10 μA, etc) until the antenna is no longeroscillating (e.g., in the Q-enhanced region). The tuned bias current canbe pre-stored as the second bias current for the receive mode. Inselecting the first bias current, the bias current may be tuned to theoscillation region and a current range in which the antenna power isoptimal may be selected as the first bias current. It should beunderstood that other suitable methods may be used for selecting thebias current for the receive mode and/or the transmit mode.

In operation, the communication device 202 of the present disclosureutilizes the same driver circuit 222 for operating the antenna 214 inthe receive mode and the transmit mode. To receive signals, thecommunication controller 218 operates the driver circuit 222 as anamplifier by having the bias circuit 220 output the second bias currentto the driver circuit 222. As discussed above, the cross-coupledtransistors of the driver circuit 222 form two inverting amplifiersaround the antenna 214 and substantially reduce the resistive lossassociated with the antenna 214. By reducing the resistive loss, thedriver circuit 222 increases the quality-factor of the antenna 214 andthus, increases the sensitivity and communication range of the antenna214.

In the receive mode, the cross-coupled pairs are biased in anon-oscillating region (e.g., bias current <20 μA) as opposed to theoscillation region (bias current >100 μA). This increases the qualityfactor of the resonant tank (e.g., from 110 to 300), which results in avoltage gain (e.g., 49 dB voltage gain at 43 μW). As an amplifier, thedriver circuit replaces the high power low noise amplifier (LNA) andbulky off-chip channel select filter to prevent the re-radiation of asuper-regenerative receiver. The bias current of the cross-coupled paircan be digitally tuned with a tail transistor.

As it relates to the example embodiment in FIG. 7, the amplifier isfollowed by a 2-stage amplifier and a 32-stage rectifier serves as anenvelope detector (ED). The demodulation of the 2-PPM signal sent fromgateway is to compare the energy at each pulse position. One can avoidsetting a threshold voltage for comparators and have better interferencetolerance. Different from the parallel resonant in the transmit mode,the antenna and the tuning capacitor forms a series resonant circuit, sothe received voltage will be amplified by Q-times. The bias current isset with enough back-off margin to ensure its stability. The boosted-Qgives us extra 20 dB gain at RF with very low power consumption. Inaddition, because of the high-Q tank, one can have a highly selectivefront-end filter response, which increases the receiver blockertolerance and eliminates the need of an off-chip channel selectionfilter. Another advantage of Q-enhanced amplifier is that it does nothave the oscillation period that is typical in the super-regenerativereceiver. As a result, there is no re-radiation issue with the proposedamplifier. So one can safely co-design the amplifier with antenna anddon't need an isolation amplifier which is typically used in thesuper-regenerative receiver.

When the communication controller 218 is instructed to transmit a signal(e.g. data signal) by the sensor controller 204, the communicationcontroller 218 operates the driver circuit 222 as an oscillator byhaving the bias circuit 220 output the first bias current to the drivercircuit 222. In response to the first bias current, the cross-coupledtransistors operate to oscillate the antenna 214 to transmit a signal atthe resonant frequency of the antenna 214.

In the transmit mode, in lieu of a power amplifier (PA) and a phaselocked loop (PLL), the communication device 202 utilizes the drivercircuit 222 to resonate the antenna 214 at, for example, 915 MHz with aquality factor (Q) of 110. While the open-loop operation may result incarrier frequency drift, the gateway can be reconfigured to have a widerfrequency search. Thus, the communication device of the presentdisclosure may reduce the overall power consumption of the communicationdevice and increase the communication range of the sensor device.

The peak transmitter current may exceed the battery current limit, andtherefore the transceiver, in the transmit mode, may operate from a 0.5μF storage cap when C₃ and C₄ (FIG. 4) are series-connected while thebattery, under the protection of the current limiter, continuallycharges the storage cap. The relatively long storage cap recharge timebetween transmit pulses results in inherent sparsity that can beutilized to realize a new energy-efficient modulation scheme thatconveys multi-rate trellis-coded bits in the form of sparse M-ary PPM.In the transmit mode, the baseband controller supports dynamicallyadjustable modulation parameters such as the pulse width, number ofpulse repetition, trellis-code rate (¼, ⅓, ½, 1, 2, 3, 4) for errorcorrection, and PPM modulation size M.

As it relates to the example embodiment in FIG. 7, the basebandcontroller will directly modulate the EN_TX signal to transmit the M-PPMsignal. The transmitter is a power oscillator with antenna as theresonant component with 4V supply to maximize the output power. Ittransmits the signal through parallel amplification of the current flowsthrough the antenna coil. The advantage of this structure is that wedon't need an additional carrier frequency generation (local oscillator)circuitry, which saves a lot of power. The intrinsically high-Q antennalowers the power consumption of oscillation and the measured efficiencyis 32%. In order to maximize the Q of oscillation tank, one can use ahigh-Q off-chip SMD capacitor as the coarse frequency tuning component.In this embodiment, a two on-chip capacitor banks is sued for fine-rangefrequency tuning. One major disadvantage of this free-running oscillatorapproach is the carrier frequency drift although the carrier frequencydrift can be tracked by the powerful signal processing on the gateway.

Since the gateway can be much more powerful and larger than the sensornode, it has less constraint on power budget. The gateway can even bepowered directly from the electrical outlet. The proposed networktopology is a star network, every sensor node will link to a nearbygateway. The gateway will collect data from sensor nodes and upload to acloud server via WiFi. In this communication network scheme, the gatewayhas excellent receiver sensitivity, strong transmitter power and digitalsignal processing ability. Therefore, in the idle state, the sensor nodeis sleeping in order to save energy, while the gateway receiver isalways listening to find a nearby sensor node. Further details regardinga similar communication protocol may be found in the article “A 10 mm³inductive coupling radio for syringe-implantable smart sensor nodes”,IEEE Journal of Solid-State Circuits, Vol. 51, NO. 11 (November 2016)which is incorporated in its entirety by reference.

FIG. 9 shows a timing diagram for the protocol. The synchronization isperformed on the gateway, so the gateway is adapting to the baseband andcarrier frequency offset on the sensor node. In addition, the gatewaywill analyze the channel and reconfigure the sensor node with optimalsettings according to different environment. It is referred to as linkadaptation.

Sensor node first initiates the communication by sending headers.Gateway is continuously listening to the channel until it finds a validheader. After the header is received, the gateway starts analyzing andcalculating the frequency offset. There is a pre-defined waiting time insensor node, waiting for gateway synchronization. In this period,gateway estimates and adjusts its baseband timing and carrier frequency.After the waiting time, the gateway is perfectly synchronized to thesensor node and it will send a return packet with link updates commend.For saving the energy, the receiver on the sensor node will only turn onfor a pre-defined return packet length and perform a very simplesampling and decoding process. No synchronization process is needed atthe sensor node. So in order to send the return packet to sensor node,gateway needs to track the pre-defined waiting time while doing thecalibration and sends out the packet on time. Otherwise, it will missthe sensor node receiver turn-on period and the communication will fail.

For multiple node access, the header from each sensor node is generatedfrom different pseudo-noise code (PN code) on the sensor node to supportmultiple access scheme. The signal coding scheme of the sensor nodetransmitter is the convolutional coding, which supports multiple codingrate (4, 3, 2, 1, ½, ⅓, ¼) in different environment. The system supportsdifferent parameters that are re-configurable on-the-fly, such as pulsewidth, pulse repetition, and coding rate. As a result, we can doon-the-fly trade-off between data rate and link distance. It isunderstood that other communication protocols fall within the broaderaspects of this disclosure.

FIG. 10A shows the tuning range of the transmitter in the exampleembodiment. The x-axis is tuning thermometer code, the y-axis is carrierfrequency. An on-chip capacitor bank is used for tuning. It has 14tuning bits with 40 MHz tuning range. FIG. 10B is the measured EIRP as afunction of the transmitter bias current. The maximum EIRP was measuredat −27 dBm with 500 μA bias current, including the antenna efficiency.The peak power consumption is 2 mW from 4V.

FIG. 11 is the sensitivity as a function of Q-enhanced amplifier biascurrent. Because the front-end is co-designed with antenna and notimpedance-matched to 50 Ω, it cannot do the wired test. The receiversensitivity was measured wirelessly after initially transmitting headersto the gateway and performing gateway synchronization. The sensitivitywas measured −93 dBm at 30 kbps data rate with 10⁻³ BER. Because of ourreceiver sampling and demodulation scheme, the single-tone blocker willnot affect our system. The measured modulated blocker from 3 MHz to 10MHz offset is shown in FIG. 12. The system has good blocker tolerancethanks to the Q-enhanced technique. Recall that one needs to performgateway synchronization before receiving packet. In fact, the blockertolerance performance is limited by the gateway being false triggered bythe strong blocker.

Spatial and functional relationships between elements (for example,between modules, circuit elements, semiconductor layers, etc.) aredescribed using various terms, including “connected,” “engaged,”“coupled,” “adjacent,” “next to,” “on top of,” “above,” “below,” and“disposed.” Unless explicitly described as being “direct,” when arelationship between first and second elements is described in the abovedisclosure, that relationship can be a direct relationship where noother intervening elements are present between the first and secondelements, but can also be an indirect relationship where one or moreintervening elements are present (either spatially or functionally)between the first and second elements. As used herein, the phrase atleast one of A, B, and C should be construed to mean a logical (A OR BOR C), using a non-exclusive logical OR, and should not be construed tomean “at least one of A, at least one of B, and at least one of C.”

In the figures, the direction of an arrow, as indicated by thearrowhead, generally demonstrates the flow of information (such as dataor instructions) that is of interest to the illustration. For example,when element A and element B exchange a variety of information butinformation transmitted from element A to element B is relevant to theillustration, the arrow may point from element A to element B. Thisunidirectional arrow does not imply that no other information istransmitted from element B to element A. Further, for information sentfrom element A to element B, element B may send requests for, or receiptacknowledgements of, the information to element A.

In this application, including the definitions below, the term “module”or the term “controller” may be replaced with the term “circuit.” Theterm “module” or “controller” may refer to, be part of, or include: anApplication Specific Integrated Circuit (ASIC); a digital, analog, ormixed analog/digital discrete circuit; a digital, analog, or mixedanalog/digital integrated circuit; a combinational logic circuit; afield programmable gate array (FPGA); a processor circuit (shared,dedicated, or group) that executes code; a memory circuit (shared,dedicated, or group) that stores code executed by the processor circuit;other suitable hardware components that provide the describedfunctionality; or a combination of some or all of the above, such as ina system-on-chip.

The module may include one or more interface circuits. In some examples,the interface circuits may include wired or wireless interfaces that areconnected to a local area network (LAN), the Internet, a wide areanetwork (WAN), or combinations thereof. The functionality of any givenmodule of the present disclosure may be distributed among multiplemodules that are connected via interface circuits. For example, multiplemodules may allow load balancing. In a further example, a server (alsoknown as remote, or cloud) module may accomplish some functionality onbehalf of a client module.

The term code, as used above, may include software, firmware, and/ormicrocode, and may refer to programs, routines, functions, classes, datastructures, and/or objects. The term shared processor circuitencompasses a single processor circuit that executes some or all codefrom multiple modules. The term group processor circuit encompasses aprocessor circuit that, in combination with additional processorcircuits, executes some or all code from one or more modules. Referencesto multiple processor circuits encompass multiple processor circuits ondiscrete dies, multiple processor circuits on a single die, multiplecores of a single processor circuit, multiple threads of a singleprocessor circuit, or a combination of the above. The term shared memorycircuit encompasses a single memory circuit that stores some or all codefrom multiple modules. The term group memory circuit encompasses amemory circuit that, in combination with additional memories, storessome or all code from one or more modules.

The term memory circuit is a subset of the term computer-readablemedium. The term computer-readable medium, as used herein, does notencompass transitory electrical or electromagnetic signals propagatingthrough a medium (such as on a carrier wave); the term computer-readablemedium may therefore be considered tangible and non-transitory.Non-limiting examples of a non-transitory computer-readable medium arenonvolatile memory circuits (such as a flash memory circuit, an erasableprogrammable read-only memory circuit, or a mask read-only memorycircuit), volatile memory circuits (such as a static random accessmemory circuit or a dynamic random access memory circuit), magneticstorage media (such as an analog or digital magnetic tape or a hard diskdrive), and optical storage media (such as a CD, a DVD, or a Blu-rayDisc).

The apparatuses and methods described in this application may bepartially or fully implemented by a special purpose computer created byconfiguring a general purpose computer to execute one or more particularfunctions embodied in computer programs. The functional blocks andflowchart elements described above serve as software specifications,which can be translated into the computer programs by the routine workof a skilled technician or programmer.

The computer programs include processor-executable instructions that arestored on at least one non-transitory computer-readable medium. Thecomputer programs may also include or rely on stored data. The computerprograms may encompass a basic input/output system (BIOS) that interactswith hardware of the special purpose computer, device drivers thatinteract with particular devices of the special purpose computer, one ormore operating systems, user applications, background services,background applications, etc.

The foregoing description of the embodiments has been provided for thepurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the disclosure, and all such modificationsare intended to be included within the scope of the disclosure.

What is claimed is:
 1. A wireless communication device for a sensorapparatus, comprising: an antenna; a driver circuit electrically coupledto the antenna and includes at least one pair of cross-coupledtransistors; and a bias circuit electrically coupled to the drivercircuit, wherein the bias circuit operates, in a transmit mode, to biasthe driver circuit with a first bias current, and operates, in a receivemode, to bias the driver circuit with a second bias current, such thatthe first bias current differs from the second bias current, wherein thedriver circuit, in response to the first bias current, oscillates theantenna and, in response to the second bias current, amplifies a signalreceived by the antenna.
 2. The wireless communication device of claim 1wherein the antenna is further defined as a loop antenna.
 3. Thewireless communication device of claim 1 wherein the driver circuit isfurther defined as a pair of NMOS field effect transistors cross-coupledto each other and coupled in parallel with the antenna.
 4. The wirelesscommunication device of claim 1 wherein the driver circuit is furtherdefined as a Colpitts oscillator.
 5. The wireless communication deviceof claim 1 wherein the driver circuit is further defined as a first pairof NMOS field effect transistors cross-coupled to each other and coupledin parallel with the antenna, and a second pair of PMOS field effecttransistors cross-coupled to each other and coupled in parallel with theantenna, wherein the bias circuit biases the first pair of NMOS fieldeffect transistors.
 6. The wireless communication device of claim 1wherein the second bias current has a magnitude set to substantiallycancel resistive loss of the antenna and the first bias current has amagnitude larger than the second bias current.
 7. The wirelesscommunication device of claim 1 further comprises a frequency tuningcircuit electrically coupled in parallel with the antenna and the tuningcircuit includes at least one capacitor electrically coupled in parallelwith the antenna.
 8. The wireless communication device of claim 1further comprises a controller interfaced with the bias circuit.
 9. Thewireless communication device of claim 1 is integrated into a sensordevice, wherein the sensor device includes the antenna sandwichedbetween two circuit boards, the driver circuit mounted to one of the twocircuit boards and the bias circuit mounted to one of the two circuitboards.
 10. A wireless communication device for a sensor apparatus,comprising: an antenna having inductive impedance; a driver circuitelectrically coupled to in parallel with the antenna and including apair of cross-coupled transistors; and a bias circuit electricallycoupled to the driver circuit, wherein the bias circuit operates, in atransmit mode, to bias the driver circuit with a first bias current, andoperates, in a receive mode, to bias the driver circuit with a secondbias current, such that the second bias current has a magnitude set tosubstantially cancel resistive loss of the antenna and thereby increasequality factor of the antenna during the receive mode, wherein thedriver circuit, in response to the first bias current, oscillates theantenna and, in response to the second bias current, amplifies a signalreceived by the antenna.
 11. The wireless communication device of claim10 wherein the antenna is further defined as a loop antenna.
 12. Thewireless communication device of claim 11 further comprises a frequencytuning circuit electrically coupled in parallel with the antenna and thetuning circuit includes at least one capacitor electrically coupled inparallel with the antenna.
 13. The wireless communication device ofclaim 12 wherein the driver circuit is further defined as a pair of NMOSfield effect transistors cross-coupled to each other and coupled inparallel with the antenna, where gates of each transistor is coupled todrain of the other transistor, drains of each transistor are coupled tothe antenna and sources of each transistor are coupled to the biascircuit.
 13. The wireless communication device of claim 12 wherein thedriver circuit is further defined as a Colpitts oscillator.
 14. Thewireless communication device of claim 12 wherein the driver circuit isfurther defined as a first pair of NMOS field effect transistorscross-coupled to each other and coupled in parallel with the antenna,and a second pair of PMOS field effect transistors cross-coupled to eachother and coupled in parallel with the antenna, wherein the bias circuitbiases the first pair of NMOS field effect transistors.
 15. The wirelesscommunication device of claim 112 is integrated into a sensor device,wherein the sensor device includes the antenna sandwiched between twocircuit boards, the driver circuit mounted to one of the two circuitboards and the bias circuit mounted to one of the two circuit boards.